The world wide web ("the web") is a very large body of information maintained on thousands of computer systems connected by the Internet. The web is organized into millions of documents called web pages. A group of related web pages produced and maintained by the same person or organization is known as a "web site."
A user typically interacts with the web using an application program known as a web browser or web client executing on the user's computer system. Each web page may be independently accessed by providing a reference to the web page, called a "URL," or "uniform resource locator," to the web browser application. URLs are well known, and are discussed in detail in T. Berners-Lee, et al., Uniform Resource Locators (URL), RFC 1738, CERN, Xerox PARC, Univ. of Minn., December, 1994The web browser uses the URL to retrieve the contents of the web page via the Internet using a Hypertext Transfer Protocol (HTTP), then displays those contents in a window displayed by the web browser application. HTTP is well known, and is discussed in detail in R. Fielding et al., Hypertext Transfer Protocol--HTTP/1.1, RFC 2068, Univ. of Col., MIT Laboratory for Computer Science, Digital Equipment Corp., January 1997. Web page contents are generally expressed in Hypertext Markup Language (HTML), and can include data such as text, still images, and audio and video clips; programs executable on the client machine; and links to related web pages. HTML is well known, and is discussed in detail in T. Bernes-Lee, et al., Hypertext Markup Language--2.0, RFC, 1866, MIT Laboratory for Computer Science, November 1995. Because web page contents can be extensive and the bandwidth available to download them is often limited, some web pages require considerable amounts of time to download.
Because the web is decentralized and diverse, some web pages may contain content that is objectionable to some users. For example, some web pages contain depictions of nudity, violence, or sex that may be inappropriate for young users.
Some web pages may also contain executable computer program code ("code") that is unsafe to execute. For example, a web page may contain code that is maliciously destructive and erases or modifies data stored on the user's computer system when it is executed. A web page may further contain code that, while not maliciously destructive, was carelessly developed and contains serious bugs.
Given the availability of objectionable content and unsafe code via the web, an automatic yet overrideable approach to screening out objectionable content and unsafe code would have significant utility, especially if it did not further exacerbate long download times for desired content and code.